Method of establishing a warp joint of a stranded wire and stranded wires used therein

ABSTRACT

A method of establishing a wrap joint of a stranded wire consisting of a strand of a plurality of wires twisted together, wherein said stranded wire is wrapped around a terminal rod in a direction opposite to the direction of twist thereof. A stranded wire consisting of a strand of a plurality of wires and an insulating sheath covering said strand, said strand being twisted to such an extent that it will not be untwisted in the sheath stripping operation and further coated with a conductive material as required.

United States Patent Moriyama et al.

[ 3,688,811 Sept. 5, 1972 54] METHOD OF ESTABLISHING A WARP JOINT or A STRANDED WIRE AND STRANDED wIREs USED THEREIN [72] Inventors: Kunimasa Moriyama, 2758-14, lijimacho; Tomio Kogure; Kozi Sakai, both of 3514, Totsukamachi, all of Totsuka-ku, Yokohama; Keisaku Takeuchi, 204-48, Kamisugata, Kohoku-ku, Yokohama, all of Japan [22] Filed: March 6, 1970 [21] App1.No.: 17,050

[30] Foreign Application Priority Data March 12, 1969 Japan ..44/183l4 [52] US. Cl. ..140/11l, 29/628, 140/149, 242/7.17

[51] Int. Cl. ..B2lf 15/00 [58] Field of Search ..140/71.6, 93, 111, 149, 104; 242/7.l7; 29/628, 505, 202.5, 203; 57/144,

[56] References Cited UNITED STATES PATENTS 2,439,465 4/1948 Gookin /93 3,237,300 3/1966 Townsend et al ..81/9.5 2,132,235 10/1938 Green 1 74/128 2,760,731 8/1956 Belek ..242/7. 17 3,410,078 1 l/ 1968 Freedman et al ..57/

Primary ExaminerLowell A. Larson Attorney-Craig and Antonelli [57] ABSTRACT A method of establishing a wrap joint of a stranded wire consisting of a strand of a plurality of wires twisted together, wherein said stranded wire is wrapped around a terminal rod in a direction opposite to the direction of twist thereof.

A stranded wire consisting of a strand of a plurality of wires and an insulating sheath covering said strand, said strand being twisted to such an extent that it will not be untwisted in the sheath stripping operation and further coated with a conductive material as required.

2 Claims, 8 Drawing Figures METHOD OF ESTABLISHING A WARP JOINT OF A STRANDED WIRE AND STRANDED WIRES USED THEREIN The present invention relates to a method of establishing a wrap joint of a stranded wire and to a stranded wire used therein.

Wrap joint is being widely used in a variety of electric and electronic apparatuses, owing to its high reliability and high workability. However, the application of the wrap joint has heretofore been limited only to a single-core wire.

In a complicate electronic apparatus, because of its extensive wiring, cables are frequently used and moreover a casing of a gate type is occasionally employed. In such a case, it becomes necessary to use a multicore cable or a stranded wire, which has brought about the inconvenience that the wrap joint cannot be applied.

An object of the present invention, therefore, is to make the wrap joint of a stranded wire possible and thereby to enable the electric wire connections in various types of apparatuses to be achieved entirely by wrap joint.

Another object of the invention is to provide a wrap joint of a stranded wire which is less inferior in its characteristics, such as contact resistance and wrapping strength, to the wrap joint of a solid wire, and also to provide a stranded wire suitable to such wrap joint.

The above objects can be attained by the following features of the present invention. Namely, the first feature of the invention resides in the fact that a stranded wire is wrapped around a terminal rod in a direction opposite to the direction of twist of the stranded wire. By so doing, it is possible to prevent untwisting of the stranded cable after said stranded wire has been wrapped by means of a wrapping tool, and to increase the wrapping strength of the wire.

The second feature of the invention resides in the fact that the stranded wire used is twisted at a high pitch so as to enhance the effect of the first feature set forth above, whereby it is possible to ease the insertion of the wire into the wrapping tool, to increase the wrapping strength and to obtain a wrap joint of small contact resistance.

The third feature of the invention resides in the fact that the stranded wire used is coated, for example, with solder, tin or silver. By so doing, it is possible to obtain exactly the same characteristics as those of a wrap joint ofa solid wire.

These and other objects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, which show embodiments of the invention and in which:

FIG. 1 is a perspective view showing a stranded wire lapped around a terminal rod;

FIG. 2 is an illustrative view for explaining the method of wrapping the stranded wire as shown in FIG.

FIG. 3 is a perspective view showing an embodiment of the stranded wire used in the present invention;

FIG. 4 is a circuit diagram showing a method of measuring the contact resistance of the wrap joint;

FIG. 5 is an illustrative view showing a method of measuring the wrapping strength of the stranded wire;

FIG. 6 is a graph showing the contact resistances measured of wrap joints of various types of wires;

FIG. 7 is a graph showing the wrapping strengths measured of wrap joints of various types of wires; and

FIG. 8 is a cross-sectional view showing another embodiment of the stranded wire.

Referring to FIG. 1, there is shown a stranded wire 11 wrapped around a terminal rod 13 fixed to an insulating base 12. The wrapping of the stranded wire can be achieved, using a wrapping tool of the type known in the art. Namely, first of all the stranded wire is stripped in a length necessary for-wrapping, by' removing an insulating sheath 11a, which in the art is called stripping operation. Then, the length of the exposed wire is inserted into a wire insertion slot provided in the wrapping tool and the terminal rod is received into a terminal insertion hole of said tool, and thereafter the wire is wrapped around the terminal rod. What should be noted here is the correlation between the direction of twist of the stranded wire 11 and the wire wrapping direction. According to the embodiment shown in FIG. 1, the direction of twist of the stranded wire 11 (the direction in which, when twisted, the individual wires are tightened, as viewed from the cut end face 11b of the stranded wire) is counterclockwise, whereas the direction in which the stranded wire is wrapped is clockwise. This correlation is explicitly shown in FIG. 2. Namely, in FIG. 2 reference numeral 24 indicates the direction of twist of the stranded wire and 22 indicates the direction in which the stranded wire is wrapped. FIG. 2 shows only one pitch of the stranded wire which consists of seven individual wires twisted together. By wrapping the stranded wire in a direction opposite to the direction of twist thereof, the following effects can be obtained:

In general, when a conductor is wrapped around a terminal rod by means of a wrapping tool, the outer diameter of the resultant coil of wrapped conductor is larger than the inner diameter of the same, when looking axially of the terminal rod. However, in the wrapping operation to form a wrap joint, since the conductor is merely inserted into the slot of the wrapping tool and retained therein with freedom of rotation, the conductor turns as it is wrapped, so as to escape from being elongated and it is not the case that a fixed portion of the wire, located at the outer periphery of the coil is elongated incident to the wrapping operation. Explaining this with reference to FIG. 2 which shows a portion, corresponding to one pitch, of the stranded wire of the present invention, the length 1 of the outer diameter and the length 1 of the inner'diameter of that portion of the stranded wire are in the relation of I 1 but considering the individual wires, the lengths thereof of the wrapped portion of the stranded wire are all the same. Namely, with the arrow 21 indicating the direction in which the wrapping proceeds and the arrow 22 indicating the direction in which the wrapping tool is rotated, the stranded wire 11 is wrapped while being twisted in the direction of arrow 23. Thus, it will be seen that if the stranded wire is wrapped in such a manner that the direction of arrow 23 and the direction of twist of the stranded wire, indicated by the arrow 24, become the same, the stranded wire will be wrapped without being untwisted but with the twist of the wire rather increasing somewhat. On the contrary, if the relation'between the direction of twist of the stranded wire and the wire wrapping direction is reversed, the stranded wire will be untwisted as it is wrapped around the tenninal rod, and the contact resistance, the wrapping strength and the appearance of the wrapjoint will be largely degraded thereby. This may be avoided by making the twist of the wire extremely tight but in this case, the softness and flexibility inherent to the stranded wire will be lost.

Next, methods and measures to further enhance the effect of the present invention will be explained hereinafter:

l To reduce the pitch of twist It is considered that the characteristics of a stranded wire get closer to that of a solid wire as the pitch of twist thereof becomes smaller. Therefore, by making small the pitch of twist of the stranded wire in the method of this invention, the following advantage can be obtained.

At all events, if the stranded wire is previously twisted at a high pitch at the time of inserting it into the slot of the wrapping tool, there will be the advantages that the insertion of the wire into the slot is facilitated and that the wrapping strength of the resultant wrap joint becomes large and contact resistance of the same becomes small.

2. To coat the stranded wire with a conductive material The method of this invention can be practiced more effectively, by the use of a stranded wire coated with a conductive material.

FIG. 3 shows a stranded wire 11 which is manufactured by a method comprising twisting seven bare wires 31 of the same diameter together in a counterclockwise direction at a predetermined pitch, coating the resultant strand with a conductive material 32 and then covering the same with an insulating sheath 11a. As the conductive material 32, solder, and tin, silver and alloys thereof are preferably used, but other metals and alloys may optionally be used. The thickness of the coating is optional but need not be so large.

The use of a stranded wire coated with a conductive material as described above is advantageous in that untwisting of the wire, resulting from the stripping or wrapping operation, can completely be avoided, in that the wrapping strength of the resultant wrap joint can be increased, and in that a workability and characteristic exactly the sameas in the case of a single-core wire can be obtained. In addition, the stranded wire thus coated with a conductive material has such a secondary advantage that when it is used for soldered joint, the operation of twisting the wire end at the time of soldering can be eliminated and the operation of providing a priming solder can even be eliminated particularly when the wire is coated with solder or tin.

Now, an example of the present invention wherein the method of the invention was practiced using several types of stranded wires individually, will be illustrated hereunder in comparison with the conventional wrap joint of a solid wire:

In this example, use was made of seven different types of stranded wires as indicated in the table below, all of which consisted of seven bare wires having a diameter of 0.18 mm and twisted together in a counterclockwise direction at a pitch of mm.

Coating of Material of Strand Conductive Material Presence Material 1 Sofi Copper No Sofi Copper for 3 wires 2 No Hard copper for 4 wires 3 Hard copper 4 Sofl copper Yes Tin 5 Hard copper 6 Soft copper Solder 7 Hard copper The wire used for comparison with the abovedescribed stranded wires was a tin plated soft copper wire having a diameter of 0.5 mm which is commonly used for wrap joint.

These wires were individually wrapped around a 1 mm X 1 mm square terminal rod 7.5 turns by means of a wrapping tool operating at 4,000 r.p.m., and the contact resistance and wrapping strength of each wrap joint were measured by the methods shown in FIGS. 4 and 5 respectively. Namely, the contact resistance was measured by conducting a current of mA from a 6 V DC. power source 41 through a variable resistor 42, an ammeter 43, a sample wire 44 and a terminal rod 45, and measuring a potential difference V (mV) across the opposite ends of the wrapped portion of the wire by a voltmeter 46 and then dividing the value of the measured potential difference by 100. On the other hand, the wrapping strength was measured by abutting a load gauge 54 against the wrapped portion 53 of the wire around a terminal rod 52 extending from a base 51, as shown in FIG. 5, pushing the base 51 toward the load gauge 54 while holding said load gauge stationary, and reading the load, applied to the base, on the load gauge at the point when the wrapped portion 53 begins skid on the terminal rod.

FIGS. 6 and 7 respectively show the average values of contact resistance and wrapping strength of the individual wrap joints measured by the methods described above. As will be apparent from these graphs, the contact resistance of each stranded wire according to the present invention is substantially equal to that of the conventional solid wire, indicating that the stranded wires of this invention do not have a particular problem in this respect, and the wrapping strengths of the stranded wires of this invention are not substantially inferior to that of the conventional solid wire, except for the wrapping strength of the uncoated stranded wire consisting of soft copper wires. The value of wrapping strength of the uncoated stranded wire of soft copper is yet high enough for the practical use of said wire in an apparatus wherein the requirement for reliability and the conditions under which the stranded wire is used are not so severe, and further the value can readily be increased as by increasing the number of turns of the wrapped wire or by changing the shape of the terminal rod.

Although the present invention has been described and illustrated herein above in terms of stranded wires consisting of wires of same diameter twisted together, it is to be understood that the invention can, of course, be applied to stranded wires consisting of wires of different diameter wires twisted concentrically or twisted together. An example of such stranded wires is shown in FIG. 8. The stranded wire shown in FIG. 8 is composed of a core wire 81 which may be of such a diameter that the wire itself is not adapted to wrap joint, fine wires 82 wrapped around the core wire 81 and an insustranded wire a plurality of turns around a terminal rod in a direction opposite to the direction of twist thereof.

2. A method of establishing a wrap joint of a stranded wire according to claim 1 characterized in that said stranded wire is further provided with a coating of conductive material.

l t l 

1. A method of establishing a wrap joint of a stranded wire consisting of a plurality of wires twisted together in a high pitch, which comprises wrapping said stranded wire a plurality of turns around a terminal rod in a direction opposite to the direction of twist thereof.
 2. A method of establishing a wrap joint of a stranded wire according to claim 1 characterized in that said stranded wire is further provided with a coating of conductive material. 